WEDNESDAY, Nov. 2, 2016 -- Three injections of a therapeutic vaccine may control genital herpes as effectively as daily pills for at least a year, a new study suggests.

Researchers tested the experimental vaccine in 310 people with herpes from 17 centers around the United States. The three shots, administered three weeks apart, appeared to reduce patients' genital lesions and the process of "viral shedding" in which they can spread the disease through sexual contact.

Infectious disease experts hailed the vaccine as a promising development in the treatment of genital herpes. The incurable disease affects about one in every six people ages 14 to 49 in the United States, according to the U.S. Centers for Disease Control and Prevention.

"In general terms, people receiving [the vaccine] have greater than 50 percent fewer days in which virus is present in their genital tracts, which in theory may reduce transmission," said study author Jessica Baker Flechtner. She's chief scientific officer at Genocea Biosciences, the Cambridge, Mass., manufacturer of the vaccine.

"However, this would need to be proven in a well-powered clinical trial," she added. "Our trials have included both men and women, and to date, we have not seen a difference in the vaccine impact between genders."

Currently named GEN-003, the vaccine is believed to work by prompting a type of white blood cell known as a T-cell to recognize and kill cells in which the virus lives, Flechtner explained.

Patients were randomly split into seven dosing groups, including a placebo group.

Testing was repeated periodically for 12 months after dosing and included analyzing genital swab samples for the presence of the herpes virus. The days when genital lesions were present were also recorded.

Current herpes treatment involves taking antiviral pills that can control the length and severity of symptoms and reduce patients' outbreaks. But many patients struggle with taking their treatments regularly, infectious disease experts said.

"The antiviral drugs available for use orally are pretty good and very safe, but they don't work on everybody, and some find it very hard to take on a daily basis," said Dr. Lawrence Stanberry. He is chair of pediatrics at Columbia University Medical Center/New York-Presbyterian Morgan Stanley Children's Hospital in New York City.

"Some patients aren't very good about taking medication every day, and some don't like to for herpes because they say it's intrusive and reminds them they have genital herpes," added Stanberry, who was involved in herpes research for many years. "Regrettably, there's still a stigma... but some say a vaccine wouldn't remind them on a constant basis about their illness."

Stanberry agreed with Dr. Matthew Hoffman, of Christiana Care Health System in Wilmington, Del., that it would take at least several years until the experimental vaccine might become widely available. The U.S. Food and Drug Administration has yet to approve the vaccine, a process that requires additional successful clinical trials.

The most common side effects patients experienced after vaccination included muscle aches, fatigue and pain or tenderness at the injection site. No patients experienced life-threatening reactions, Flechtner said.

Hoffman called the vaccine "an exciting, novel approach" to genital herpes treatment, noting that it enables patients' own immune systems to "come to the rescue and create chronic suppression."

It could also positively influence patients' intimate relationships, he said, which can be dramatically affected by herpes flare-ups.

"Herpes is an uncomfortable, embarrassing disease," Hoffman said. "This [vaccine] offers the opportunity to protect people going into new relationships.

"As you can imagine, if one partner has six to 10 episodes of herpes per year and the other partner is unaffected, it can really change the nature of the relationship," he added. "But if that number goes down to one to two episodes per year based on immunization, it can help protect the other partner."

Stanberry predicted that future research would look at combining the vaccine with antiviral pills to gauge the impact on reducing sexual transmission. On its own, the vaccine "is likely to reduce the risk, but the likelihood of eliminating the risk is exceedingly small," he said.

The study was presented at the Infectious Disease Society of America's annual meeting in New Orleans that ended Oct. 30. Research presented at conferences typically hasn't been peer-reviewed or published, and results are considered preliminary.

More information

The American College of Obstetricians and Gynecologists answers frequently asked questions about genital herpes.